1. Field of the Invention
This invention relates generally to an artificial illumination control system for photographic apparatus and, more particularly, to an artificial illumination control system for controlling the energization of a source of artificial illumination in a "fill-in flash" mode of operation where ambient light levels are relatively high, but portions of the photographic subject are relatively dark.
2. Description of the Prior Art
When taking a photograph under conditions at which the levels of ambient light intensity are relatively high but portions of the photographic subjects are relatively dark, it may be desirable to provide additional scene illumination from a source of artificial illumination such as a flashbulb or from an electronic flash device sometimes referred to as a "strobe" unit. Situations where a source of artificial illumination are used in relatively high ambient light levels are commonly referred to as "fill-in flash" mode operation as more fully described in a U.S. Pat. No. 3,610,122 entitled "Shutter Timing System" issued Oct. 5, 1971, by C. H. Biber and assigned in common herewith. Automatic photographic exposure control systems of the type typically configured to combine a light sensitive timing network and a voltage sensitive triggering circuit, or the like, in controlling relationship with a shutter assembly may also be utilized in photographic situations requiring a "fill-in flash" form of illumination. Such automatic exposure control systems are capable of providing full control over the regulation of a "fill-in flash" exposure interval and must also be compatible for operation with artificial illumination under scene conditions representing relatively low ambient light levels.
In order to facilitate automatic exposure control, it is generally preferable that the shutter blade elements assume their maximum effective aperture defining position prior to the energization of a source of artificial illumination. Thus, the artificial light source may be triggered to illuminate upon the closing of a triggering switch as one of the shutter blade elements moves into its light unblocking terminal position as more fully described in U.S. Pat. No. 3,610,122 supra.
Photographic apparatus have recently embodied so-called "follow focus systems" which depend upon the principle that the anticipated light level at a camera will depend upon the known characteristics of the artificial light source which is used and upon the distance of the subject being photographed to the artificial light source. Thus, in shutter blade systems of the scanning type, the mechanism for opening and closing a continuously variable exposure aperture is coupled to the lens focusing system of the camera which moves the lens system in accordance with the distance from the lens to subject being photographed. As the lens system is moved to provide the correct focus for a particular distance from the camera to the subject, the coupling mechanism of the follow focus control system also moves to determine an appropriate maximum exposure opening in response to the focusing action, and the maximum aperture is limited in accordance with anticipated light level at the scene to be photographed. Hence, the maximum aperture to which the shutter blade elements move may vary with lens focusing, and thus it may become impractical to utilize a switch to signal the movement of the shutter blade elements to their largest aperture defining position.
Instead, a time delay circuit responsive to the initiation of the exposure interval may be utilized to energize the artificial light source when the shutter blade elements reach their largest aperture defining position regardless of lens focusing or follow focus setting. However, under conditions of relatively high levels of ambient light intensity where the artificial light source is utilized for "fill-in flash" mode purposes, the predetermined time delay may terminate after the desired film exposure. Thus, during the "fill-in flash" mode of operation, film could become overexposed from the high levels of ambient light intensity prior to the predetermined time delay required to energize the artificial light source subsequent to the initiation of the exposure interval.
Therefore, a primary object of this invention is to provide a control system for a source of artificial illumination which may be utilized in either low levels of ambient light intensity or high levels of ambient light intensity for "fill-in flash" mode operation.
It is a further object of this invention to provide an automatic artificial illumination control system compatible for operation with an automatic exposure control system for providing a correct exposure with artificial illumination regardless of the levels of ambient light intensity.
It is an additional object of this invention to provide an automatic artificial illumination control system for energizing a source of artificial illumination as a function of whichever of two predetermined events first occurs.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.